This invention relates to lubricant compositions for transmission of power, and more particularly to lubricant compositions having excellent durability and high traction coefficient and can be utilized effectively for practical purpose as lubricants for power transmission having a traction drive mechanism.
In recent years, traction drive (friction driving device utilizing rolling contact) is employed as continuously variable transmission for automobile and industrial equipment, etc. As the fluid used for the traction drive, a fluid having high traction coefficient and high power transmitting efficiency is required.
Under the circumstances, a variety of proposals are made in order to obtain fluid for traction drive having high power transmitting efficiency (for example, Japanese Patent Publications Nos. 46-338, 46-339, 47-35763, 53-36105, 58-27838, Japanese Patent Laid-open Publications Nos. 55-40726, 55-43108, 55-60596, 55-78089, 55-78095, 57-155295, 57-155296, 57-162795 and the like).
It is necessary to lubricate the traction drive mechanism with a single oil since said traction drive mechanism is constituted as an apparatus for transmission of power containing gear mechanism, oil pressure mechanism, rolling bearings, etc. in the same system.
However, the lubricants for transmission of power mentioned above are not useful for practical purposes, if they do not give durability to metal materials which constitute the traction drive mechanism, gears, bearings and the like. To give the durability to the materials, it is indispensable to render excellent load carrying capacity and wear resistance against the metal material and to prolong the fatigue life of the metal material in addition to the foregoing characteristics, and moreover, it is necessary that lubricant has satisfactory oxidation stability of the lubricant and particularly, has no generation of sludge. And yet, the lubricant gives preferably excellent rust resistance against the metal material without disturbing these performances.
However, the conventional fluid for traction drive enumerated in the foregoing deteriorates the durability of the metal material constituting the traction drive mechanism, gears, bearings and the like remarkably although its power transmitting efficiency is improved, and is not suitable for use due to occurrence of seizure, wear or fatigue damage or deteriorates the thermal oxidation stability of the lubricant, and particularly, does not withstand sufficiently for practical use because of operation defect upon generation of a large amount of sludge.
Under the circumstances, in order to overcome the foregoing conventional problems, blending of the additives such as extreme pressure additive, antiwear agent, antioxidant to the fluid for traction drive described in the foregoing is considered.
But, when an additive such as extreme pressure additive is merely added to the fluid for traction drive, problems such as shortening the fatigue life of the traction drive mechanism or remarkably deteriorating the power transmitting efficiency or causing corrosion, and as a result, the lubricant capable of satisfying sufficiently all the characteristics which are appropriate for practical purpose has not been available.